Typically, printers require a supply of a print medium, such as paper, to be loaded into the printer and controllably moved through the printer. The paper is typically supplied as either a continuous stream of paper or as individual sheets. The paper is fed into the printer using a set of drive rollers which frictionally engage the paper and propel it through the printer along a predetermined path. The drive rollers often are driven by a stepper motor which drives the drive rollers in small increments or steps such that the paper is propelled incrementally or stepped through the printer, pausing slightly between each step. As the paper is stepped through the printer, it passes a conventional printhead having a linear array of elements, such as a thermal printhead or an inkjet printhead. During each pause between steps, a small portion of the paper is aligned with the printhead and selected elements of the printhead are activated to produce a portion of an image on the portion of the paper aligned with the printhead.
This image portion is a small portion of an entire image to be printed. The entire image typically is produced by stepping the paper past the printhead, pausing the paper after each step, determining a step number (e.g., fifth step or sixth step) corresponding to the pause, determining the portion of the image corresponding to the step number, determining which elements of the printhead to activate to produce the determined portion of the image, and activating the determined elements to produce the determined portion of the image on the paper. A microprocessor controls the operation.
To produce the entire image accurately, the distance the paper is propelled for each step must be controlled precisely. Further, the step number must be monitored continuously to enable the location of the paper relative to the printhead to be precisely determined.
This control of the paper position and monitoring of the step number is typically achieved with a stepper motor with precisely defined step sizes and by digitally controlling the stepper motor with a microprocessor motor controller. The timing of the printer must also be controlled accurately, so that the printhead is activated during the pauses between steps.
The need for such stepper motors, digital controllers and timing control greatly increase the weight, complexity and cost of printers. Also, monitoring the step number and correlating it to the controlled stepping of the stepper motor and the image portion requires considerable microprocessor time.